Email delivery delay - Yahoo

Email delivery delay - Yahoo

It seems there is a HUGE issue with emails being delivered to Yahoo addresses.  When I send a message to a yahoo address it has a time delay of around 4 hours. 
I'm guessing the problem is the Zoho servers, but are you aware of other email providers (e.g. hotmail) doing the same.

I know this is definately happening as I've tested it myself yesterday and today - I have customers who use Yahoo and email is time sensitive so what is an alternative?